Dumbbell



FIG. 1 is a front perspective view of a dumbbell of my design;

FIG. 2 is a front elevational view thereof, with the rear elevational view, top plan view and bottom plan view being the same; and,

FIG. 3 is a right end elevational view thereof, with the left end elevational view being the same. 

The ornamental design for a dumbbell, as shown and described. 